Method and apparatus for forming workpieces



April 13, 1965 E. L. CHRISTIAN ETAL. 3,177,689

METHOD AND APPARATUS FOR FORMING WORKPIECES Filed 001,. 9, 1961 Hel lll

s Il lil NVEN'TORS EARL L. CHRISTIAN DONALD G. DE VLIEG BY Mal/L am AT EY vantages over the prior formation practices.

3,177,689 METHQD AND APPARATUS FR FORMNG WRKHECES Earl Landon Christian, San Diego, and Donald Gerard De Vlieg, La Mesa, Calit., assignors to General Dynaniics Corporation, San Diego, Calif., a corporation of Delaware i Filed Get. 9, 1961, Ser. No. 143,844 3 Claims. (Cl. '72-S6) This invention relates generally to the formation of workpieces, such as sheet metal blanks, and particularly to formation by the application of pressure, and is directed to a novel forming method to be carried out by a novel forming apparatus.

Heretotore, the formation oi metal workpieces has been accomplished by the utilization of conventional metallic dies and hydraulic presses. Several disadvantages are inherent in such formation practice. Formation of large workpieces requires the provision of heavy, costly forming apparatus. In such cases, the dies used must be very thick and strong with large attendant weight to withstand the pressures to which they are subjected. For example, a onepiece die casting used to` form aluminum domes for radar reiiector antennas measures seventy/*eight inches in diameter with a twenty-two inch contour depth, and weighs twenty tons. Fabrication of a die of this sizeusually requires approximately two to three weeks of time. Furthermore, very heavy handling equipment must be used to position the die for `forming workpieces. Owing to these and other factors it is readily apparent that the provision of apparatus necessary to form objects heretofore involved great initial expenditures of money and costly subsequent maintenance and handling expenses.

The present invention resides in apparatus and method for formation of materials to assure the precise conguration of the forming surface of a die as a result of the pressure applied thereto by the application oi shock waves generated by an ignited explosive change within a pressure transmitted medium.

In contrast the present invention provides distinct ad- One advantage is that less costly dies can be used, providing savings from sixty-tive to eighty-tive percent of the cost of conventional steel dies. Another advantage is that the weight of equipment utilized is considerably reduced. For example, the hereinbefore mentioned conventional stee die weighing twenty tons could be replaced by a die wall weighing only two hundred and titty pounds.-

Where it took two or three weeks to provide conventional'dies in previous forming practices, the present invention utilizes forming members which can be available in two or three days. With the much lighter apparatus used, handling of parts can be accomplished mostly by hand, requiring little use of heavy handling equipment such as cranes.

Accordingly, it is an object of this invention to provide novel apparatus and method for forming workpieces to desired shapes.

Another object of the present invention resides in the provision of novel apparatus and method capable of forming workpieces to desired shapes simply and economically.

Still another object of the present invention is the provision of novel apparatus and method to form materials by utilizing pressure.

A further object of the invention is to provide for the forming of materials by the use of light weight forming parts which are readily available and easy to handle.

An object of the present invention is to provide novel nited States Patent l ICS forming apparatus incorporating novel die forming means.

These and other objects and advantages of the invention will be more readily apparent to those skilled in the art from the following description of speciiic apparatus embodying and utilizing the novel method.

In the drawings:

The single ligure is a partial cross-sectional view taken through the apparatus of the present invention.

Referring now to the single iigure of the drawings, the apparatus associated with the present invention is generally designated by the numeral 1th and comprises a die arrangement 12, a workpiece 14, a body ot pressure transmitting medium 16, and shock wave generating apparatus 18.

The diearrangement 12 generally includes a metallic container 20, a thin die wall 22, a draw ring 24, and a plurality of clamps 26. The container Ztl is shown as being open-ended and includes an upright cylindrical wall 28 and a circular bottom wall Sti, but could be ot any predetermined height, size or contour. Adjacent the open end of the container there is provided a circumferential flange 32 which carries an annular resilient seal element 34 positioned as by bonding in an appropriate circular groove.

The die wall 22 is illustrated as being shaped to form a hemispherical cavity 36, but could be any desirable shape depending on the contour desired to be imparted to the workpiece 14 to be formed. The die wall is provided with a flat annular flange portion 38 and can be of any size as long as it iscapable of being positioned with the `flange portion 33 overlying the seal element 36% in the containerilange 32, as shown, to provide an enclosed space 40. The die wall is preferably of laminated glass cloth, or the like. The die wall could be of molded plastic material or thin sheet metal.

A control valve 42 controls the iiow of non-compressible fluid 44 from a source (not shown) through a suitable Huid line to the enclosed space 40 to back up the die wall 22, as shown. The iluid is preferably water or the like.

An air relief valve 46 connects to a passage 48 in the wall 23 of the container and serves as a means to exhaust air from the space 40 as the iluid 42 is admitted thereto through the valve 42 to ensure complete evacuation of air, as will hereinafter be more fully disclosed.

A length of flexible tubing Sil, preferably of rubber, or the like, is suitably connected to the lowermost point in the cavity 36 and a control valve 52 positioned on the container outwardly of the space (it). The lexible tubing 5t) can be of any desired length, as long as it has suiiicient length to facilitate connection of the die wall 22 thereto prior to positioning of the die wall on the container in preparation for forming. The control valve 52 is adapted to be connected by a suitable fluid line to apparatus capable of exhausting air from the cavity 36, such as a vacuum pump (not shown).

The shock wave generating apparatus 18 consists of an explosive change or squib Se. The squib can comprise any well known explosive substance such as dynamite, trinitrotoluene, or the like, suitably enclosed as in a plastic casing, or the like. A pair of electrical conduit wires S6 and 58 extend upwardly to a detonation generator (not shown), which is capable of generating electric current to actuate a detonator in the squib to deteriorate the explosive therein. A wire 6i?, suitably attached to the squib and support means (not shown), serves to position the squib in the pressure transmitting medium 16 at a predetermined distance from the die arrangement.

In the practice of the invention, a thin, light weight die wall 22 is prepared with a cavity having the desired is contour. The die wall is then attached to the tubing 50 and placed over the open end of the container 20 with its flange portion 38 upon the container flange 32. The workpiece 14, to be formed, is placed upon the die wall 22 to cover the cavity 36. The Vdraw ring 24 is then positioned upon the workpiece and the clamps 26 slipped over theedges of the parts and tightened by means of screws 62. When the clamps are adequately tightened, pressure sealing is effected between the die wall flange 38 and the container flange 32 by means of the seal element 34. The die wall flange 38 and the workpiece 14 achieve their own sealing between adjacent contact surfaces due to the tightening force of the clamps 26, and a restraining force'is applied to the workpiece, as will be hereinafter more clearly apparent. Next, with both valves 42 and 46 opened, water from the source (not shown) is allowed to flow through the valve 42 into the space 40 until the space is completely lled with the 'water to back the die wall 22, and all air has been evacuated from the space through passage 48 and the valve 46. This condition will be achieved when it is observed Y that waterflows from the space 4t), through the passage 48, and out the valve 45. Immediately, upon observation of water flow from the valve 46, both valves 42 and 46 are closed. Air is then evacuated from the cavity V36 through the tubing 50 and valve 52 by means of the vacuum pump (not shown). The valve 52 is then closed and the assembled die apparatus is lowered into the pressure transmitting medium 16 in any desirable manner. The squib 54 is next located in the pressure transmitting medium in proper relations to the workpiece by means of the .wire 60. The detonation generator (not shown), is then actuated, kthereby detonating the squib 54. When the squib 54 is detonated, shock waves are produced through the` medium 16. waves contact the workpiece 14, there is an extremely rapid, downward movement of that portion of the workpiece 14 above the cavity 36 into the cavity, thus forming the workpiece. As this forming takes place the restraining force of the draw ring 24 upon the workpiece is adequate to permit the dragging of the workpiece into the cavity, but will prevent any tendency of the workpiece to wrinkle during the forming action. Also, during this forming action, since the die wall 22 is backed by the incompressible medium 44, any tendency of the die wall to move or distort as the workpiece is urged into the cavity 36 is adequately prevented, thus assuring perfect formation of the workpiece.,

As described, the present invention is characterized as being simple, rapid, and economical in the formation of materials into desired shapes wherein a workpiece is caused to assume the shape of a thin diel wall backed by an incompressible fluid by means of explosive energy produced in a pressure transmitting medium wherein the y workpiece and die wall are submerged.

Although only the preferred embodiment of the invention has been disclosed, it is to be understood that the As the shock invention is not limited thereto, as many variations and modifications will be apparent to those skilled in the art, and the invention is to be given the broadest possible interpretation within the scope and terms of the following claims.

What we claim is:

1. A method of forming comprising placing a thin inflexible die wall over an opening in a container, placing a workpiece over one side of said die wall to deue an air space therebetween, securing the edges of said die wall and workpiece to said container to ellect sealing therebetween, completely filling said container withwan incompressible fluid to immovably back the other side of said die wall, evacuating air from said air space, immersing said die wall, container, and workpiece in a liquid adjacent an explosive charge, and igniting said explosive charge to produce shock waves in said liquid forcing said workpiece against said die wall.

2. Forming apparatus comprising a container having ank opening, a thin inflexible die wall positioned over said opening, means for securing the edges of said die wall and a workpiece to said container to effect sealing therebetween, said die wall and workpiece defining an air space therebetween, an incompressible fluid completely iilling said container to immovably back said die wall, means for evacuating air from the space between said die wall and workpiece, a body of liquid, an explosive charge in said liquid, said die wall, container, and workpiece being immersed in said liquid adjacent said explosive charge, and means for igniting said explosive charge to produce shock waves in said liquid forcing said workpiece against said die wall.

3. A forming die comprising a container having an opening, a thin inflexible die wall vpositioned oversaid opening, means for securing the edges of said die wall and a workpiece positioned over said die wall ,to said container to effect sealing therebetween, an incompressible fluid completely filling said container to immovably back said die wall, and means for evacuating air from the space between said die wall and workpiece.

References Cited by the Examiner UNITED STATES PATENTS 2,317,869 4/ 43 Walton 113-44 2,344,743 3/ 44 Smith 113-44 2,367,779 1/ 45 Hull 113-44 2,401,299 6/46 Glavin 113-44 2,410,857 11/46 l Ahern 113-44 2,783,728 3/57 Hoffmann 113-44 2,935,03 8 5 60 Chatten 113-44 2,969,758 1/ 61 Howlett et al. 113-44 2,983,242 5/ 61 Cole 29-421 CHARLES W. LANHAM, Primary Examiner.

NEDWIN BERGER, WILLIAM J. STEPHENSON,

Examiners. 

1. A METHOD OF FORMING COMPRISING PLACING A THIN INFLEXIBLE DIE WALL OVER AN OPENING IN A CONTAINER, PLACING A WORKPIECE OVER ONE SIDE OF SAID DIE WALL TO DEFINE AN AIR SPACE THEREBETWEEN, SECURING THE EDGES OF SAID DIE WALL AND WORKPIECE TO SAID CONTAINER TO EFFECT SEALING THEREBETWEEN, COMPLETELY FILLING SAID CONTAINER WITH AN INCOMPRESSIBLE FLUID TO IMMOVABLY BACK THE OTHER SIDE OF SAID DIE WALL, EVACUATING AIR FROM SAID AIR SPACE, IMMERSING SAID DIE WALL, CONTAINER, AND WORKPIECE IN A 